Attenuation of sound waves including ultrasonic waves propagating through the air is temperature dependent. The object detection performance of an ultrasonic object detection apparatus may therefore vary with a change in temperature. According to Patent Literature 1, temperature data is acquired from a temperature sensor provided outside an ultrasonic sensor of a vehicle to calculate a correction amount.
An outside air temperature sensor in a vehicle is generally provided for an air conditioner and commonly installed inside the engine room. It is known that temperatures cannot always be measured accurately because of the engine exhaust heat and the like. In the case of a malfunction, the outside air temperature sensor cannot detect temperatures correctly. In the case that the outside air temperature sensor fails to detect temperatures accurately, if the sensitivity setting of the ultrasonic sensor is based on the temperature acquired from the measurement of the outside air temperature sensor, the ultrasonic wave reception will be made with a wrong sensor sensitivity, which will lower the object detection accuracy.